A known electrophotographic image forming apparatus, removably sets therein a developing cartridge configured to hold toner, as a developing agent. Such an image forming apparatus is generally provided with a detection device that determines whether the developing cartridge is installed in the image forming apparatus. When it is determined that the developing cartridge is not installed in the image forming apparatus, the apparatus indicates as such, to prevent a printing operation from being performed with the developing cartridge uninstalled. For example, Japanese Laid-Open Patent Publication No. 5-35097 discloses an electrophotographic apparatus in which installation of the developing cartridge is detected by an optical sensor (toner empty sensor).
For example, Japanese Laid-Open Patent Publication No. 2003-84645 discloses an image forming apparatus including a photoconductive cartridge having a photoconductive element as an image carrier, and a developing cartridge removably installed in the photoconductive cartridge. In the image forming apparatus, the photoconductive cartridge and the developing cartridge are independent of each other, so that the photoconductive cartridge and the developing cartridge can be replaced separately at their appropriate timing, achieving cost efficiency.
Even when the structure disclosed in Japanese Laid-Open Patent Publication No. 5-35097 is applied to the image forming apparatus disclosed in Japanese Laid-Open Patent Publication No. 2003-84645, installation/uninstallation of the photoconductive cartridge cannot be detected. More specifically, when the developing cartridge is not installed in the image forming apparatus, it cannot be determined whether neither the photoconductive cartridge nor the developing cartridge is installed in the image forming apparatus or whether only the developing cartridge is not installed in the image forming apparatus even though the photoconductive cartridge is properly installed in the image forming apparatus.